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Chapter 4, Xgig TraceControl Capture Configuration General Settings
98 Xgig Analyzer User’s Guide
Choosing an Auto Option for 12G SAS Blades
When you set the Link Speed to Auto (12G/6G/3G) , the analyzer is able to auto-detect any of these
three data rates. In the 3G and 6G cases, the analyzer uses oversampling to detect the data rate.
12G traffic is captured directly. 6G traffic is oversampled 2x, and 3G traffic is oversampled 4x.
This setting provides flexibility if you do not know the data rate of the link under test. However,
note that if the traffic is at a 3G data rate, then oversampling by 4x can cause false bit errors. In this
case, it is better to change the Link Speed to
3G
fixed or
Auto (SAS 6/3G)
and reinitialize the link
under test.
When you set the Link Speed to
Auto (12G/6G)
, the analyzer is able to auto-detect either 12G or
6G data rates. In the case of 6G, the analyzer uses oversampling to detect the data rate. 12G traffic
is captured directly. 6G traffic is oversampled 2x, and 3G traffic is not detected. This setting
provides flexibility if you do not know whether the data rate of the link under test is 6G or 12G.
However, note that if the traffic is at a 6G data rate, then oversampling by 2x may not be ideal. If
the analyzer shows bit errors, then try setting Link Speed to
6G fixed or Auto (SAS 6/3G) .
When you set the Link Speed to
Auto (6G/3G)
, the analyzer is able to auto-detect either 6G or 3G
data rates. In the case of 3G, the analyzer uses oversampling to detect the data rate. 6G traffic is
captured directly. 3G traffic is oversampled 2x, and 12G traffic is not detected. This setting
provides flexibility if you do not know whether the data rate of the link under test is 3G or 6G.
However, note that if the traffic is at a 3G data rate, then oversampling by 2x may not be ideal. If
the analyzer shows bit errors, then try setting Link Speed to
3G fixed.
For the
Auto
options, no actual negotiation or handshake takes place between the analyzer and any
external device – the blade ports merely detect the data speed from the speed negotiation sequence
happening on the link. The
Auto
options can automatically determine the idle link speed only if
the Xgig ports see the link initialization activities that take place (for example, OOB and speed
negotiation events). If link initialization sequence does not happen while an
Auto
option is set, the
blade will retain its existing speed. The auto-detect option automatically detects the link speed
when the analyzer is idle. Once a capture is started, the auto-detect feature does not change the
current analyzer speed if the link does change. The data rate will be fixed by the analyzer during
capture.
PCIe Link Speeds
For PCIe, the link speed can be set to the highest rate supported by the blade containing the ports,
or a supported lower rate. Available rates for Xgig PCIe, in GT/s, are 2.5 (Gen1), 5.0 (Gen2), and
8.0 (Gen3). You can also select
Auto
, and the Xgig will select the correct speed based on the
device under test, and if it cannot, it will default to 8.0 (Gen3).
Link Speeds for 10G Multi-Function Blades
No link-speed options will appear for ports on 10 Gigabit Multi-Function blades including the
Xgig5000 10G Ethernet blade; the speed is fixed at 10.3125 Gbps for Gigabit Ethernet and
10.5187 Gbps for Fibre Channel and cannot be changed.